A variety of produce bags have been developed for being filled by automatic produce packing machines. Some produce bags also are formed from an open mesh material such as a woven natural or synthetic fiber, a knitted fiber, or a synthetic resin fabric mesh, such as the fabric of cross-laminated synthetic resin fibers known as Cross Laminated Airy Fabric or (CLAF) from BP Amoco. CLAF is an open mesh material of cross-laminated warp and weft strands or fibers of synthetic resin. Open mesh bags are particularly useful for storing produce that must have access to fresh air to preserve the shelf life of the produce.
However, problems have been found to occur when wicket holes are formed in fabric for hanging the bags from pegs or “wicket pins” of automatic produce bag filling purposes. Slits are typically formed in the mesh in the vicinity of the wicket holes. The slits lead away from the wicket holes in order to aid in tearing the bag away from the packing machine once the bag is filled with product. When the mesh fabric is slit for this purpose, only a certain number of synthetic resin fiber strands in the mesh fabric are left uncut. The remaining uncut fiber strands are the sole support for the bag when it is suspended from the wicket pins or pegs and filled with product. The number of strands that remain uncut is variable and indeterminate, and the reliability of the bags for use in automatic packing machines suffers. Bags with too many cut strands do not have adequate strength and tear off from the wickets during filling operations. Bags with an inadequate number of cut threads may fail to pull away from the wickets after the bags are filled.
Another disadvantage of all-mesh bags is that they cannot be printed upon using printing techniques commonly used to print indicia on resin films. Those having a desire to print information on mesh bags therefore often apply a so-called “print band” on the bag to display the desired information.
Composite bags, formed of a synthetic resin mesh sheet and a synthetic resin film sheet, have been proposed. These bags are typically referred to as “half and half bags” because one side or “half” is formed from an open mesh material and a second side or “half” is formed from a clear, tinted, or colored film. It is important to mention that the term “half” does not require that each material must form an equal percentage of the bag's surface area. Indeed, half and half bags can be formed with gusseted sides or four-sided structures, leading to the use of a substantially greater percentage of one of the materials than the other. The mesh sides of half and half bags provide the breathability required of many products, whereas the film side presents a convenient surface for the printing of advertising or other information. Half and half bags having at least some of these characteristics are disclosed, for example, in U.S. Pat. No. 3,257,915, U.S. Pat. No. 6,190,044 (the '044 patent), G.B. Pub. Pat. App. No. 2,309,956, and J.P. Pub. Pat. App. No. 60-24743. Half and half bags are also commercially available, e.g., from Volm Bag, Inc. of Antigo, Wis. and Kenneth Fox Supply Co. of McAllen, Tex.
Some half and half bags are also configured to be filled by wicketed automatic bag filling equipment. For instance, Volm Bag offers a half and half bag having wicket holes on the film side of the bag. The '044 patent discloses a half and half bag having a film strip on the upper edge of the bag that is configured to have wicket holes formed through it without suffering the drawbacks normally associated with forming wicket holes in a mesh structure. Kenneth Fox Supply Co., the assignee of the '044 patent, offers a similar bag commercially.
Another problem associated with half and half bags is that they tend to have relatively weak side seams because the aggregate joined area between the mesh and the film is relatively small due to the open structure of the mesh. This problem is especially detrimental at the upper end of the bag, which is typically subjected to the greatest stress during bag filling. It is at this location that clamps or other structures physically pull the bag apart to open the bag in preparation for a filling operation. Operation of this equipment imposes considerable stress at the upper ends of the seams. Additional stress is imposed on the seams when the produce or other packaged products fall into the bag from above. Prior half and half bags exhibited substantially higher fill failure rates than similarly constructed all mesh bags or all film bags.
As discussed in the '044 patent, this problem can be partially alleviated by providing a so-called “reinforcing strip” of a resin film on the upper end of the mesh side of the bag. In the configuration proposed in the '044 patent, the upper end of the mesh side of the bag is sandwiched between the reinforcing strip and the film side of the bag, and the three overlapping portions are bonded together. The reinforcing strip disclosed in the '044 patent also extends above the top of the mesh wall of the bag and has wicket holes formed through it for hanging the bag from the wickets of an automatic bag filling machine. According to the text of the '044 patent, the overlapping resin film wall and reinforcing strip fuse directly together at the seams, enclosing the fiber strands between them. This is said to increase the strength of the seams at the upper or top corner portions of the bag.
However, it has been discovered that the problem of side seam weakness is not adequately addressed by the reinforcing strip design of the '044 patent. The reinforcing strip is sealed to the bag's film side wall only along that portion of the bag in which the reinforcing strip overlaps the bag's mesh side wall. In fact, because the upper edge of the bag's film side is coplanar with the upper edge of the bag's mesh side, there is no film material above the upper edge of the bag's film side for the reinforcing strip to bond to. There is no direct film-to-film bond above the upper end of the bag's mesh side. It has been discovered that the resultant seam is relatively weak, possibly due to the fact that sandwiching of the mesh material between the two strips of film material leads to the remnants of relatively large interstices or gaps between adjacent sections of film material, even after the bonding process. Hence, the amount of film-to-film sealing is relatively small. Testing of bags of that type has revealed a relatively high failure rate during bag filling.
Another drawback of the bag disclosed in the '044 patent is that the mesh side wall of the bag is necessarily the rear side wall, i.e., the one having the wicket holes formed therein. The reinforcing strip is not configured to be accessed by suction cups or other devices commonly used to open a bag in preparation for filling. It is believed that the '044 patent stresses this relationship because it is not contemplated that the reinforcing strip can also be used as a suction surface for the suction cups. Instead, it is believed that the '044 patent considers the resin film side wall of the bag to form the only suitable surface for engagement by suction cups. This requirement to form the rear side wall of the bag from the mesh material places limits on diversity of bag design and on the versatility of bag filling processes.
The need therefore has arisen to provide a composite mesh/film bag having relatively strong seams, particularly at the upper ends of those seams.
The need has also arisen to provide a composite open mesh/film bag design that does not necessarily require that the mesh side wall of the bag be the rear side wall.